The present invention relates to catheters that can be placed in bodily conduits. The invention particularly relates to coronary dilatation catheters for use in administering treatments to widen constricted blood flow passages typically caused by stenoses in, for example, heart valves or coronary arteries.
A stenosis is a region of a blood vessel which has been narrowed to such a degree that blood flow is restricted. If the stenosis is severe, treatment is required to restore adequate blood flow, and often such treatment requires surgery or angioplasty. Transluminal angioplasty is a procedure for treating a patient having a stenosis or constricted region in a coronary artery. Frequently the stenosis can be expanded so that the artery will permit an acceptable blood flow rate.
Coronary angioplasty includes the insertion of a balloon catheter through a patient's artery to the arterial stenosis and injecting a suitable fluid into the balloon to inflate it. The inflated balloon expands the stenosis radially outwardly and compressing it against the artery wall to increase the cross-sectional area of the artery so that the artery has an acceptable blood flow rate. Angioplasty has become a successful alternative to coronary arterial bypass surgery.
Ordinary balloon catheters have a balloon fastened around the exterior of a tubular shaft, with the balloon in fluid flow relation with the interior of the shaft. The shaft provides a conduit for fluid inflation medium to inflate the balloon.
Known, so-called "balloon-on-a-wire" catheter devices are designed using a thin walled steel tube with a small diameter core wire, e.g. of solid steel, extending from its proximal end to its distal end. The distal end of the angioplasty balloon is attached near the distal end of the core wire, and a plastic sleeve extending over the core wire covers a joint between the proximal end of the balloon and the distal end of the steel tube. In such a catheter, the steel tube acts as the shaft of the device to provide pushability and torque to the core wire. The distal segment of the catheter, including the core wire, balloon, and sleeve extension, acts as the flexible portion of the device, capable of traversing tortuous anatomies.
One of the greatest disadvantages of this known design is the stiffness of the shaft tubing, which can result in difficulty in negotiating tortuous anatomies. Additionally, the thin walled steel tubing has a tendency to kink too easily during the process of pushing the catheter to thread it through the arteries. This kinking can lead to fracturing and separation at the kink points in the steel tubing. The stiffness of the tubing also reduces the uniformity of the torque rotation of the shaft in a curved or bent configuration. In this design, there is also an abrupt transition between the stiff shaft portion and the flexible distal portion of the catheter.
In some variations of this balloon-on-a-wire design, the distal core wire is allowed to extend completely through the inside diameter of the proximal tube to strengthen and reinforce the tubing and to act as a safety wire within the device in case of catastrophic failure of the catheter, for example complete fracture of the shaft. However, the presence of this core wire reduces the cross-sectional area of the lumen within the shaft available for inflation of the balloon. The presence of the core wire also dramatically increases the exposed surface area within the lumen, resulting in increased fluid drag and pressure loss along the length of the lumen. The decreases in both cross-sectional area and inflation pressure result in a significant increase in the time required to inflate and deflate the balloon which, in turn, limits its maximum practicable size.
In another context, medical devices are known which employ highly flexible coils, including cross-wound multifilar (CWMF) coils. For example, a CWMF coil may be used as a flexible guidewire tip to facilitate manipulation of a medical device into a selected precise position within a bodily passage. Alternatively, a known catheter-like guidewire includes a CWMF coil and a core wire. The CWMF coil is sheathed in a polymeric jacket to within a short distance from the distal tip of the device. Fluid medication may be administered to a bodily passage by seepage from a central lumen through the CWMF coil. This device is not intended for dilatation, and includes no dilatation balloon. Even if such a balloon were added at the distal region of the device, the seepage mechanism would not provide sufficiently rapid inflation and deflation of the balloon.
It would be desirable to have a balloon-on-a-wire type of dilatation catheter which is kink-resistant, is easily maneuvered through tortuous anatomies, provides improved safety and torqueability, and permits rapid inflation and deflation of the dilatation balloon and larger balloon sizes. The catheter described herein was developed to address that need.